Portable circular saws, either pneumatically or electrically powered, are among the most common hand tools. They are used extensively by carpenters and many other tradesmen in a variety of industries such as building construction. They are also widely used by homeowners and other "do-it-yourselfers."
The use of a portable circular saw to cut materials such as wood, asbestos/cement, fiber board and the like generates large amounts of sawdust. This dust fills the atmosphere surrounding the workplace and settles on surfaces at the workplace. The airborne dust represents a health hazard when breathed in by the user of the saw and other people in the immediate vicinity. Settling of the dust on nearby equipment and other structures necessitates frequency cleaning of those devices. Settled dust which works into bearings and other critical parts of such devices has a detrimental effect on their operation and length of service life. Since it is impossible to prevent generation of sawdust from the operation of a portable circular saw, it is very desirable to provide means to capture that dust as soon as possible after its generation and convey it to appropriate enclosed collection and/or disposal equipment.
The portable circular saw presents a particularly difficult problem in dust capture. Unlike other saws such as rotary table saws (see e.g., U.S. Pat. No. 4,063,478) or overhead arm radial saws which operate in a single fixed location, the very nature of the use of the portable circular saw requires that it frequently be moved from one work location to another. This precludes its being enclosed in a conventional dust capture enclosure. It also requires that any dust capture device must be fully portable and capable of the same freedom of movement as the saw itself. Further, because portable circular saws are frequently used in locations where the user has only one hand free to operate the saw, any dust collection device must also be capable of operating directly in conjunction with the saw such that the user does not need to handle the dust collection device independently.
One approach to dust collection for a portable circular saw is embodied in a commercial saw produced in Germany. This saw utilizes upper and lower blade housings which are ducted to a collection system. The housings are connected by an adjustable "splitting wedge" or "riving knife" mounted in the interior of each of the housings. While this saw represents a distinct improvement in dust collection over many other units (such as that shown in U.S. Pat. No. 3,882,598, which requires use of a collection table below the saw), tests have shown it to still emit approximately twice the dust permitted by OSHA regulations. The internal location of the adjustable "splitting wedge" makes adjustment of the housings spacing difficult, which encourages users to use a wider than necessary spacing, with attendant excess dust emissions, rather than take the trouble to disassemble the saw for adjustment. The internal "splitting wedge" also serves as a dust trap and tends to cause dust clogging of the housings, and the trapped dust also complicates spacing adjustments and causes loose dust problems when the housings are disassembled for spacing adjustment.
This commercial German saw also is constructed such that air is drawn through the motor housing before it enters the dust collection housings. This serves to reduce the quantity of air effectively available to sweep dust from the vicinity of the saw blade and to prevent dust from escaping from the saw blade apertures in the upper and lower housing. The net result is that the dust collection efficiency of this saw is low.
Consequently, it would be desirable to have a shroud for a portable circular saw which would be highly effective for dust collection (i.e., would readily meet maximum dust emission regulations, such as those of OSHA), while yet being easily handled by the saw user, readily and quickly adjusted for proper housing spacing, and also capable of continuous adjustment to minor irregularities in the surface of the workpiece, thus insuring that maximum dust collection will be continuously maintained.